Chemical Vapor Deposition

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Introduction[edit]

Lecture date: Monday, 2014.09.29 (lecture recording)

CVD Basics[edit]

CVD is used to grow thin films using chemical reactions involving gaseous precursors.

CVD takes place in a flow reactor; the product is the thin film.

Precursor Activation[edit]

The precursors may be activated in several different ways:

  • thermally
    • heating of the substrate ("cold wall")
    • heating of the entire reactor ("hot wall")
    • heating of the gas ("hot filament")
  • with plasma
    • ions and electrons aid in low-temperature activation
  • with light
    • photoactivation with lasers or other light sources

Transport and Reaction Considerations[edit]

Reactions in both the gas phase and on the surface

Transport—thermal and mass—in the gas phase (convection and diffusion) and to the surface

A boundary layer will form as the gas flows over the treated surface; as boundary layer thickness increases, the resistance to transport to the surface also increases.

Deposited Film Properties[edit]

When depositing a film, you're worried about:

  • composition
  • uniformity
  • stress (due to differences in specific volume or crystal lattice structure)
  • topography (conformal? hole-filling?)

To deposit SiO₂, there are several options of precursors:

  • SiH₄ + CO₂ + H₂
  • SiCl₂H₂ + N₂O
  • SiH₄ + N₂O
  • SiH₄ + NO
  • SiH₄ + O₂

While all of these combinations may result in the same film, the film properties will be different!

Asides[edit]

A common strategy to relax stresses when growing SiO₂ films is to operate at a temperature sufficiently high to keep the SiO₂ viscoelastic so that it can flow.

References[edit]

Wikipedia pages of relevance:

YouTube videos of relevance: